Effective hormonal peptides: D-3-Pal6 -LHRH

ABSTRACT

Two sets of hormonal peptides are synthesized which are super agonists of the luteinizing hormone releasing hormone (LHRH). Chronic administration results in the inhibition of LHRH which is responsible for stimulating cell growth in the testes. One peptide has the D(dextro)-form of a monoheterocyclic amino acid in position six (D-3-pyridyl-alanine) while the other peptide has a bi-heterocyclic amino acid in that same position (β-(3-quinolyl)-D-α-alanine. Both peptides are less metabolically reactive than those in the prior art and yet both peptides are significantly more potent than LHRH itself.

BACKGROUND OF THE INVENTION

This invention concerns synthetic analogs of the peptide hormone known as the leutinizing hormone releasing hormone (LHRH). These analogs have biological potency superior to that of the LHRH which exists naturally in the hypothalamus of the human brain.

PROSTATE CANCER

Carcinoma of the prostate is the second leading cause of cancer-related deaths for adult American males who are generally over 55 years of age. About 70% of all cases of prostatic neoplasms are hormone-dependent or androgen-dependent. Prolactin may be a promoter of prostate growth. The medical treatment of prostate cancer emphasizes surgery and the therapeutic administration of estrogens and antiangrogens. Surgical castration is associated with both psychological and physiological side effects which can be extraordinarily serious. The mortality from the cardiovascular disease associated with administration of estrogens and antiandrogens can be significantly high.

Other therapeutic treatments of prostatic cancer are not satisfactorily effective, and new treatments of great superiority for prostate and other hormone related cancers are urgently needed.

AN EMERGING NEW CHEMOTHERAPY FOR PROSTATE CANCER

The synthetic analogs of LHRH which can be up to 100 times more potent than the natural LHRH have become known as "super agonists" or "super active agonists" because of their high potency. The expression "agonist" designates the intrinsic activity of a natural hormone.

Groups of investigators conducting animal studies with these super agonists of LHRH observed that the administration caused decreases in the weights of the testes, seminal vesicles and the prostate, and decreases in testosterone levels and certain receptors.

In men, two such super agonists, known as D-Trp⁶ -LHRH and D-Ser(Bu^(t))⁶ des-Gly¹⁰ -NH₂ -LHRH ethylamide were found to cause a suppression of Leydig cell function and decreases in serum levels of testosterone, dihydrotestosterone and estradiol. These reductions were observed after chronic administration of the super agonists.

CLINICAL TRIALS WITH LHRH SUPER AGONISTS IN MEN WITH PROSTATE CANCER

The observations of the effects of the super agonists of LHRH in the diverse animal studies led to clinical trials of these super agonists in men with prostate cancer in the hope that the control of prostate cancer would be far superior to any existing chemotherapy and particularly to surgery.

Apparently, the first successful palliative treatment of advanced prostatic carcinoma in man by super agonists of LHRH was carried out at the Royal Victoria Hospital in Montreal by Tollis et al. (Proc. Natl. Acad. Sci., USA, 79; 1658-1662 (1982). Both D-Trp⁶ -LHRH and D-Ser(Bu^(t))⁶ des-Gly¹⁰ -NH₂ -LHRH were administered subcutaneously in daily doses of 100 g and 50 g, respectively. In patients with urinary obstruction, there was noticeable clinical improvement. In patients with more advanced prostatic disease, the pain from bone metastases was relieved.

This collaborative trial demonstrated for the first time that super active analogs of LHRH could be beneficial therapeutic agents for prostatic cancer, and that such therapy might avoid the psychological impact of castration, even unnecessary castration, as well as the cardiovascular, hepatic, and mammotropic side effects of estrogens.

These and numerous other related studies have been reviewed by Schally et al. (Proc. Soc. Exp. Biol. Med. 175; 259-281 (1984).

THE NEED FOR NEWER SUPER AGONISTS OF LHRH FOR TREATMENT OF PROSTATIC CANCER

Obviously, D-Trp⁶ -LHRH and D-Ser(Bu^(t))⁶ des-Gly¹⁰ -NH₂ -LHRH and related super agonists such as D-Leu⁶ LHRH ethylamide had all been synthesized solely because such modifications of LHRH had higher potencies than that of LHRH itself to release the leutenizing hormone. The subsequent years of biological research of the super agonists, almost entirely in animals, unexpectedly led to the investigations of their possible use to treat prostate cancer. Actually, the acute administration of these super agonists to cause release of LH and FSH contrasts to the chronic administration which results in inhibitory effects. In this endocrinology, the inhibitory effects were paradoxical.

These past super agonists of LHRH had been fortuitously available for the prostate cancer studies in animals and in man. There is reason to believe that such fortuitous agonists will not be ultimately found to be the safest and the most effective agonists to treat prostate cancer in man.

Such analogs of LHRH are well known to have multiple endocrinological activities, and side effects, and chemical differences in stability, and enzymic breakdown when injected into man.

THE DISADVANTAGES OF CERTAIN SUPER AGONISTS OF LHRH

It is well known in peptide chemistry that certain peptides with a moiety (or more than one) of tryptophan may be unstable and discolor on storage under diverse conditions. For example, LHRH itself has Trp³ and the super agonist, D-Trp⁶ -LHRH, has Trp³ and D-Trp⁶ or the super agonist has two moieties of tryptophan which increases sensitivity to oxidation and deterioration. For acceptable medical use, a chemotherapeutic agent must have necessary chemical stability. Therefore, D-Trp⁶ -LHRH does not necessarily have the high-level of necessary stability which is requisite in chemotherapy.

D-Ser(Bu^(t))⁶ des-Gly¹⁰ -NH₂ -LHRH and D-Leu⁶ -des-Gly¹⁰ -NH₂ -ethylamide are both analogs of LHRH in which glycine has been replaced by a moiety of ethylamide. Such agonists with an N-terminal ethylamide moiety had a fleeting popularity in the field of LHRH agonists in the hope that the N-terminal of the peptide would be protected against enzymic cleavage and loss of activity. Although this aspect of enzymology is theoretically sound, such analogs may show unexpected side effects and may not necessarily be safe and effective for the treatment of prostate cancer in man over prolonged periods of time.

SUMMARY OF THE INVENTION

In this invention, two primary peptides were synthesized which have the D(dextro)-form of a monocyclic but heterocyclic amino acid in position 6 and a bicyclic but heterocyclic amino acid in position 6, respectively. The first peptide has a moiety of D-3-pyridyl-alanine in position 6 and the second peptide has the moiety of β-(3-quinolyl)-D-α-alanine in position 6. The abbreviation D-3-Pal is used for D-3-pyridylalanine and the abbreviation D-3-Qal is used for β-(3-quinolyl)-D-α-alanine.

Accordingly, these two peptides are:

I. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-GlyNH₂

II. pyroGlu-His-Trp-Ser-Tyr-D-3-Qal-Leu-Arg-Pro-GlyNH₂

Both of these two new peptides, I, II, when tested biologically, were found to be significantly more potent than LHRH itself and, therefore, these two new peptides are truly super agonists.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS

Abbreviations and Formulas

n-BuOH: n-butyl alcohol

HOAc: acetic acid

CH₃ CN: acetonitrile

KH₂ PO₄ : potassium phosphate

o-Cl-Z: o-chlorobenzyloxycarbonyl

CH₂ Cl₂ : dichloromethane

TFA: trifluoroacetic acid

Et₃ N: triethylamine

DCC: dicyclohexylcarbodiimide

DMF: dimethylformamide

i-PrOH: isopropyl alcohol

BOC: t-butyloxycarbonyl

CoF₃ : cobalt(III) fluoride

HF: hydrogen fluoride

EtOAc: ethyl acetate

Aoc: acyloxy carbonyl

Br-Z: o-bromocarbobenzoxy

Tos: P-toluenesulfonyl radical

GlnONP: glutamine-o-nitrophenol

The protected amino acids were purchased from Peninsula Laboratories, Inc., San Carlos, Calif., except for Boc-D-pCl-Phe when it was provided by the Southwest Foundation for Research and Education. ε-Amino functions were protected by the Boc-group, except for Arg which was protected by the Aoc- or the Boc-group. Side-chain functions were protected by o-Cl-Z for the ε-amino group of Lys, Tos for Arg and Br-Z for Tyr. The benzhydrylamine hydrochloride resin was purchased from Beckman Inc., Palo Alto, Calif. All solvents (except TFA and isopropanol) were distilled before use.

To test for homogeneity the peptides were chromatographed on precoated TLC plates (silica gel, Merck, Darmstadt) in the following solvent systems:

I. EtoAc:Pyr:HOAc:H₂ O=5:5:1:3;

II. n-BuOH:EtOAc:HOAc:H₂ O=2:2:1:1:;

III. n-BuOH:Pyr:HOAc:H₂ O=30:30:6:24;

IV. n-BuOH:Pyr:HOAc:H₂ O=50:33:1:40;

V. n-BuOH:HOAc:H₂ O=4:1:2

The spots on the developed thin layer plates were detected with the chlorine o-tolidine reagent.

SYNTHESIS OF THE PEPTIDES

The peptides were synthesized by the solid phase method using a Beckman Model 990 Peptide Synthesizer. The benzhydrylamine hydrochloride resin (BHA-resin) was used as a solid support. The program of the synthesizer was divided into subprograms to increase the versatility of the synthesizer, as follows:

1. Deprotection: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. 50% TFA in CH₂ Cl₂ containing 0.1% indole (1×wash, 1 or 2 min); 3. 50% TFA in CH₂ Cl₂ containing 0.1% indole (deprotection, 20 min); 4. CH₂ Cl₂ (2×wash).

2. Neutralization: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. Et₃ N (10% in CH₂ Cl₂) (2×wash, 1 or 2 min); 3. Et₃ N (10% in CH₂ Cl₂) (neutralization, 5 min); 4. CH₂ Cl₂ (2×wash, 1 or 2 min).

3. DCC Coupling: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. amino acid solution in CH₂ Cl₂ (delivery, transfer, mix, 5 min); 3. DCC (10% in CH₂ Cl₂, (delivery and mix, 180 min); 4. CH₂ Cl₂ (2×wash, 1 or 2 min).

4. Active Ester Coupling: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. amino acid solution in DMF (delivery, transfer, mix 360 min); 3. CH₂ Cl₂ (2×wash, 1 or 2 min).

5. Final Wash: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. i-PrOH (3×wash, 1 or 2 min); 3. DMF (3×wash, 1 or 2 min); 4. CH₂ Cl₂ (3×wash, 1 or 2 min).

6. Wash after TFA Treatment: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. i-PrOH (3×wash, 1 or min); CH₂ Cl₂ (3×wash, 1 or 2 min).

7. Acetylation: 1. CH₂ Cl₂ (2×wash, 1 or 2 min); 2. 10% Ac₂ O and Pyr in CH₂ Cl₂ (1×wash, 1 or 2 min); 3. 10% Ac₂ O and 10% Pyr in CH₂ Cl₂ (acetylation, 20 min); 4. CH₂ Cl₂ (2×wash, 1 or 2 min).

The first amino acid was attached to the resin by the program sequence 2-3-5. Before placing the resin into the reaction vessel, the resin was washed twice in a separatory funnel with 25 ml of CH₂ Cl₂ /g resin to remove the fine particles. In all couplings, usually a 3-4 fold excess of the Boc-amino acid over the nitrogen content of the resin (nitrogen content was about 0.5 meq/g dry resin) was used. This procedure generally resulted in a complete coupling reaction. If a positive ninhydrin color reaction was observed, a second coupling using an excess of the amino acid derivative was performed (program sequence 3-5). Then, the resin was acetylated (program sequence 7-5).

The next amino acid was attached by the program sequence 1-6-2-3-5. For DCC coupling, all amino acids were dissolved in CH₂ Cl₂. To dissolve BOC-Trp, it was necessary to add 10% DMF to the suspension. Gln was coupled to the resin by its BocGlnONP derivative using the active ester coupling program sequence 1-6-2-4-5. The Boc-GlnONP was dissolved in DMF and a few mg of 1-hydroxybenzotriazole was added as a catalyst. The volume of the solvents and the reagents used for the washing and the performing of the chemical reactions was about 10 ml/g resin. The acetylation mixture was freshly prepared before each use.

CLEAVAGE OF THE PEPTIDES FROM THE RESIN

After all of the amino acids had been coupled, the peptide resin was dried overnight, in vacuo, by an oil pump. The resin was then treated with double-distilled and dried (over CoF₃) liquid hydrogen fluoride (10 ml/g resin) containing 10-25% distilled anisole for 1 hr at 0° C. Then, the HF was evaporated under reduced pressure and the residue was dried overnight, in vacuo, by an oil pump. The mixture was then extracted twice with EtOAc (25 ml/g resin), and then twice with 25 ml of 12% HOAc, and once with 25 ml distilled, deionized water. The combined aqueous solution was lyophilized to yield the crude peptide.

PURIFICATION OF THE CRUDE PEPTIDE

Gel Filtration. 220 mg of the crude peptide was applied to a column of Sephadex G-25 (100×2.5 cm) which had been equilibrated with 12% HOAc, and then the chromatography was done with the same solvent. Fractions of 10 ml were collected. The peptide was detected by spotting samples of the individual fractions on silica gel plates and chromatographing them in solvent system V. The fractions containing the product in a partially purified state were pooled and lyophilized. The yields were in the range of 76-120 mg.

Column Chromagraphy on Silica Gel. The above lyophilized material was applied to a column of silica gel (1×60 cm), which had been equilibrated with a solvent system V and then the chromatography was done in the same solvent. Fractions of 4 ml were collected. The peptides, in general, were in elutes of fractions 30-40. The fractions which contained the pure or nearly pure peptide were collected and lyophilized. If the peptide was not sufficiently pure, it was further purified on the same column using the same solvent mixture. The yield ranged from 20-50%.

High Pressure Liquid Chromatography. The HPLC was performed on a Waters Liquid Chromatograph equipped with a Waters 660 solvent programmer. The samples were chromatographed on a chrompak Lichrosorb RP C₁₈ column (5u)(4.6×250 mm). For elution of the analogs a linear gradient from 20-100% of solvent B in 25 min. was used (solvent A: 0.1M K phosphate buffer, pH 3.0; solvent B: 30% solvent A, 70% CH₃ CH). The flow rate was 2.10 ml/min; 10 ul of a 0.1% solution of the peptide was injected. The eluted peptide was detected by its UV-absorbance at 206 mm.

Amino acid analysis. The acid analysis was performed on a Beckman Model 119 Automatic Amino Acid Analyzer. The peptides were hydrolyzed for 24 hours in a sealed glass tube at 110° C. in 6N HCl. The mixture was then dried, in vacuo. The residue was dissolved in 1.5 ml of sodium citrate buffer, pH 2.2 and 0.2 ml of the solution was applied to the analyzer.

Optical rotation. The optical rotation (αD) was measured at room temperature with a Perkin Elmer 141 Polarimeter. All peptides were dissolved in 12% HOAC (10 mg/ml or 5 mg/ml) or in MeOH.

The Determination of Purity and The Characterization. The following procedures were used for determining the purity of all the synthetic analogs: thin layer chromatography in five solvents; amino acid analysis; optical rotation; high pressure liquid chromatography.

The TLC was performed on 0.25 mm silica gel plates 60F 254 in the solvent systems I-V, as defined supra. The spots were visualized with chlorine-o-tolidine reagent.

DATA. The amino acid analytical data are:

D-Pal⁶ -LHRH: Ser 0.88(1), Glu 1.00(1), Pro 1.01(1), Gly 1.02(1), Leu 1.02(1), Tyr 1.02(1), His 0.96(1), Arg 1.00(1), Trp(+), Pal(+).

D-Qal⁶ -LHRH: Ser 0.82(1), Glu 0.89(1), Pro 1.15(1), Gly 1.13(1), Leu 1.07(1), Tyr 0.94(1), His 0.89(1), Arg 1.11(1), Trp(+), Qal(+).

The chromatographic data are in Table I.

                  TABLE I                                                          ______________________________________                                         Chromatographic Data                                                                                   Reten-                                                                         tion                                                          R.sub.f in solvent                                                                              time in Purity                                         Analog   I      II     III  IV   V     HPLC (HPLC)                             ______________________________________                                         D-       0.83   0      0.60 0.44 0.19 7.2 min.                                                                             96%                                Pal.sup.6 --LHRH                                                               D-       0.93   0.13   0.65 0.40 0.25 8.6 min.                                                                             94%                                Qal.sup.6 --LHRH                                                               ______________________________________                                    

Analogs of D-3 Pal⁶ -LHRH (1,2, and 3).

The following three analogs of D-3 Pal⁶ -LHRH were similarly synthesized and purified as:

1. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHC₃ H₇

2. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHC₂ H₅

3. pryoGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHCH₃

                                      TABLE II                                     __________________________________________________________________________     The Characterization of Analogs 1, 2, and 3                                                               TLC (R.sub.f)                                       Purification                                                                         HPLC Data            Solvent System                                      Method                                                                               min.                                                                              purity                                                                             Amino Acid Data                                                                              I  II                                                                               III                                                                               IV V                                        __________________________________________________________________________     1. (I,II,III)                                                                        18.4                                                                              19% Ser 1.05(1)                                                                          His 1.03(1)                                                                            0.98                                                                              0 0.83                                                                              0.81                                                                              0.28                                                  Glu 1.21(1)                                                                          Trp (+)                                                                  Pro 1.11(1)                                                                          Arg 1.20(1)                                                              Leu 1.16(1)                                                                          D-3-Pal (+)                                                              Tyr 1.25(1)                                                                          NH.sub.2 C.sub.3 H.sub.7 (+)                                2. (I,II,III)                                                                        16.1                                                                              99% Ser 0.68(1)                                                                          His 1.00(1)                                                                            0.98                                                                              0 0.83                                                                              0.78                                                                              0.20                                                  Glu 0.87(1)                                                                          Trp (+)                                                                  Pro 0.86(1)                                                                          Arg).87(1)                                                               Leu 0.77(1)                                                                          D-3-Pal (+)                                                              Tyr 0.86(1)                                                                          C.sub.2 H.sub.5 NH.sub.2 (+)                                3. (I,II,III)                                                                        15.8                                                                              99% Ser 0.90(1)                                                                          His 1.00(1)                                                                            0.98                                                                              0 0.80                                                                              0.75                                                                              0.16                                                  Glu 0.99(1)                                                                          Trp (+)                                                                  Pro 1.10(1)                                                                          Arg 1.04(1)                                                              Leu 0.92(1)                                                                          D-3-Pal (1)                                                              Tyr 1.05(1)                                                                          CH.sub.3 NH.sub.2 (+)                                       __________________________________________________________________________

The data in Table III are from the radioreceptor assay and allow a comparison of D-Qal⁶ -LHRH with three of the known super agonists. This assay shows that the D-Qal⁶ -LHRH is comparable with the three known super agonists for the potency of binding at a receptor and is substantially more effective than LHRH itself.

                  TABLE III                                                        ______________________________________                                         Radioreceptor Assay                                                                           Relative                                                                               Potency                                                                Potency vis-a-vis                                                              vis-a-vis                                                                              D-Lys.sup.6 --LHRH-                                                    LHRH    ethylamide                                              ______________________________________                                         D-Lys.sup.6 --LHRH-ethylamide                                                                   0.015:1   --                                                  D-Qal.sup.6 --LHRH                                                                              0.020:1   1.36:1                                              D-Trp.sup.6 --LHRH                                                                              0.011:1   0.72:1                                              D-Trp.sup.6 Pro.sup.9 Net--LHRH                                                                 0.013:1   0.86:1                                              LHRH             --        67.5:1                                              ______________________________________                                    

Receptor assay was performed by a modification of the method of Marshall, J. C., et al. Preparation of Biologically Active. I. LHRH Suitable for Membrane Binding Studies. Proc. Soc. Exptl. Biol. 149, 351 (1975).

The data in Tables IV and V are from the in vitro assay of the peptides with the pituitary incubate. This assay measures the release of LH and FSH in an in vitro system with pituitary cells from 21 day old rats. See, Bowers, C. Y. et al. on the inhibitory effects of leutinizing hormone releasing hormone analogs. Endocrinology, 106: 674 (1980).

The abbreviations are as follows: sc-subcutaneous, SEM-standard error of the mean; NS-not significant; ng-nanogram, and ml-milliliter. The p value represents the population coefficient ρ(rho) which signifies whether a sample coefficient is significant or a chance deviation from zero.

The data in Table IV show that D-Pal⁶ -LHRH and D-Qal⁶ -LHRH are essentially equivalent in activity for the release of LH at 0.1 ng and the same essential equivalents at this dosage was revealed for the release of FSH.

Comparable assays have shown that D-Qal⁶ -LHRH and D-Trp⁶ -LHRH were essentially equipotent. On this basis, D-Pal⁶ -LHRH and D-Trp⁶ -LHRH can also be considered essentially equipotent.

                                      TABLE IV                                     __________________________________________________________________________     In Vitro Pituitary Incubate Assay                                              21 Day Old Female Rat                                                                  Dosage                                                                         ng/ml                                                                               LH ng/ml                                                          Peptide medium                                                                              medium ± SEM                                                                         p value                                                                               medium ± SEM                                                                         p value                                  __________________________________________________________________________     LHRH    --   -8 ± 11      588 ± 233                                                                            --                                                0.03                                                                               52 ± 20                                                                              <.02   638 ± 292                                                                            NS                                               0.1  214 ± 30                                                                             <.001  266 ± 235                                                                            <.001                                                                              --                                           0.3  771 ± 162                                                                            <.001  4556 ± 752                                                                           <.001                                                                              --                                           1.0  1434 ± 156                                                                           <.001  8063 ± 943                                                                           <.001                                                                              --                                   D-Pal.sup.6 --LHRH                                                                      0.03                                                                               73 ± 10                                                                              <.001                                                                              NS*                                                                                  1062 ± 394 NS                                                                     NS**                                             0.1  345 ± 72                                                                             <.001                                                                              NS*                                                                               3109 ± 486                                                                           <.001                                                                              NS**                                         0.3  811 ± 182                                                                            <.001                                                                              NS*                                                                               5126 ± 967                                                                           <.001                                                                              NS**                                         1.0  1439 ± 233                                                                           <.001                                                                              NS*                                                                               9637 ± 1490                                                                          <.001                                                                              NS**                                 D-Qal.sup.6 --LHRH                                                                      0.03                                                                               47 ± 22                                                                              <.05                                                                               NS*                                                                               994 ± 181                                                                            NS  NS**                                         0.1  335 ± 37                                                                             <.001                                                                              .02*                                                                              3364 ± 364                                                                           <.001                                                                              NS**                                         0.3  611 ± 102                                                                            <001                                                                               NS*                                                                               5069 ± 751                                                                           <.001                                                                              NS**                                 __________________________________________________________________________      *Versus data for LHRH                                                          **Versus data for FSH                                                          Note: mean of 9 ± SEM                                                 

                                      TABLE V                                      __________________________________________________________________________     In Vitro Pituitary Incubate Assay                                              21 Day Old Female Rat                                                                  Dosage                                                                         ng/ml                                                                               LH ng/ml      FSH ng/ml                                           Peptide medium                                                                              medium ± SEM                                                                          p value                                                                            medium ± SEM                                                                         p value                                    __________________________________________________________________________     LHRH    --   -31 ± 63                                                                              --  156 ± 148                                                                            --                                                 .01                                                                            .03  33 ± 24                                                                               NS  598 ± 137                                                                            NS                                                 .10  206 ± 42                                                                              <.01                                                                               794 ± 52                                                                             <.001                                              .30  892 ± 92                                                                              <.001                                                                              2709 ± 252                                                                           <.001                                      D-Qal.sup.6 --LHRH                                                                     .01  104 ± 79                                                                              NS  625 ± 238                                                                            NS                                                 .03  79 ± 30                                                                               NS  638 ± 77                                                                             <.01                                               .10  647 ± 39                                                                              <.001                                                                              1890 ± 135                                                                           <.001                                      D-Trp.sup.6 --LHRH                                                                     .01  68 ± 31                                                                               NS  450 ± 64                                                                             NS                                                 .03  209 ± 74                                                                               .02                                                                               929 ± 207                                                                            <.01                                               .10  646 ± 69                                                                               <001                                                                              1714 ± 224                                                                           <.001                                                   Mean of 9 ± SEM                                                __________________________________________________________________________

Tables VI-XI summarize assays of LHRH and D-Pal⁶ -LHRH for the release of the leutinizing hormone (LH) and the follicle stimulating hormone (FSH). D-Pal⁶ -LHRH significantly released LH at a dosage of 5 ng in contrast to LHRH which was inactive at 15 ng. Correcting for the level of LH in the system before addition of the peptides, it is evident that the D-Pal⁶ -LHRH released almost 50 times as much LH as did LHRH at the dosage of 50 ng.

At a dosage of 15 ng, D-Pal⁶ -LHRH released 1270±140 ng FSH in contrast to LHRH which released only 572±68 ng.

In vivo rat assay performed by a modification of the method of Bowers, C. Y. et al. Endocrinology, 106, 674 (1980). 21 day old female rats were injected sc with saline or peptide. Blood samples for the RIAs of LH and FSH were collected at +15, +60, +120, or +180 minutes. (Tables VI-XI).

                                      TABLE VI                                     __________________________________________________________________________     In Vivo Assay in Rats                                                          For Release of LH and FSH                                                              Dosage                                                                         ng/rat                                                                             Serum LH              Serum FFSH                                   Peptide sc  ng/ml ± SEM                                                                           p value     ng/ml ± SEM                                                                         p value                              __________________________________________________________________________     LHRH    --  0.9 ± 0.7                                                                             --          227 ± 47                                          15  1.3 ± 0.2                                                                             NS  --      475 ± 43                                                                            < .01                                                                              --                                       50  3.2 ± 0.3                                                                             <.02    --  572 ± 68                                                                            .01 --                                       150 12 ± 3 <.01        839 ± 73                                                                            <.001                                D-Pal.sup.6 --LHRH                                                                     1.75                                                                               1.5 ± 0.3                                                                             NS          471 ± 128                                                                           NS                                           5   7 ± 1  <.001       738 ± 71                                                                            <.001                                        15  43 ± 7 <.001                                                                              <.001   1270 ± 140                                                                          <.001                                                                              <.001                                    50  103 ± 8                                                                               <.001   <.001                                                                              2267 ± 342                                                                          <.001                                                                              <.001                                        Mean of 9 ± SEM                                                 __________________________________________________________________________

                                      TABLE VII                                    __________________________________________________________________________     Assay in Rats for                                                              Release of LH and FSH                                                                   Dosage                                                                              LH ng/ml                                                                             Serum ± SEM                                                                         p value                                            Peptide  mg/rat sc                                                                           ± 15 min                                                                          ± 60 min                                                                            ± 15 min                                                                         ± 60 min                                   __________________________________________________________________________     LHRH     --   1.6 ± .9                                                                          1.1 ± 0.5                                                                           --   --                                                     100  49 ± 10                                                                           5.5 ± 0.9                                                                           <.001                                                                               <.01                                          D-Qal.sup.6 --LHRH                                                                       10  10.5 ± 2                                                                          49 ± 14                                                                             <.01 <.01                                                   100  37 ± 5                                                                            226 ± 36                                                                            <.001                                                                               <.001                                         D-Trp.sup.6 --LHRH                                                                       10        31 ± 6    <.001                                                  100  51 ± 10                                                                           259 ± 34                                                                            <.001                                                                               <.001                                         D-Trp.sup.6 Pro.sup.9 NET                                                               100  59 ± 10                                                                           228 ± 41                                                                            <.001                                                                               <.001                                         __________________________________________________________________________

                                      TABLE VIII                                   __________________________________________________________________________     IN VIVO Assay in Rats                                                          for Release of LH and FSH                                                              Dosage                                                                         ng/rat                                                                             Serum LH           Serum FSH                                       Peptide sc  ng/ml ± SEM                                                                            p value ng/ml ± SEM                                                                         p value                                 __________________________________________________________________________     --      --  1.7 ± 0.9   --  315 ± 186                                                                               --                                  LHRH     15 21.0 ± 4.0                                                                             --  <.001                                                                              1147 ± 489                                                                              NS                                  LHRH     50 53.9 ± 9.0  <.001                                                                              2228 ± 448                                                                          --  <.01                                LHRH    150 62.0 ± 21.0                                                                            --  <.02                                                                               1536 ± 172                                                                          --  <.001                               D-Pal.sup.6 --LHRH                                                                      15 36 ± 9  NS  <.01                                                                               1711 ± 644                                                                          NS  NS < .05                            D-Pal.sup.6 --LHRH                                                                     150 111 ± 16                                                                               NS  <.001                                                                              1591 ± 588                                                                          NS  NS .05                              ±60 min after injection of peptide or saline (-)                            --      --   1.3 ± 0.2                                                                             <.05                                                                               --  815 ± 64                                                                            <.001                                                                              --                                  LHRH    150 39.0 ± 17                                                                              --  <.05                                                                               2448 ± 209                                                                          --  <.001                               D-Pal.sup.6 --LHRH                                                                      15 81.0 ± 17                                                                              NS  <.001                                                                              1992 ± 379                                                                          NS   .01                                D-Pal.sup.6 --LHRH                                                                     150 106.0 ± 3                                                                              <.01                                                                               <.001                                                                              6432 ± 2216                                                                         NS   .02                                D-Qal.sup.6 --LHRH                                                                      15 68.0 ± 19                                                                              NS  <.01                                                                               3610 ± 363                                                                          <.05                                                                               <.001                               D-Qal.sup.6 --LHRH                                                                     150 118.0 ± 3                                                                                .001                                                                             <.001                                                                              6694 ± 2619                                                                         NS  <.05                                            Mean of 5-6 ± SEM                                               __________________________________________________________________________

                  TABLE IX                                                         ______________________________________                                         IN VIVO Assay in Rats                                                          for Release of LH and FSH                                                            Dose    Serum LH          Serum FSH                                      Peptide                                                                              ng/rat  ng/ml SEM  p value                                                                               ng/ml SEM                                                                               p value                               ______________________________________                                         --    --      1.2 ± 0.9      311 ± 36                                    LHRH   50       5 ± 0.5                                                                              --     909 ± 118                                                                            --                                          150     17 ± 3  --     1076 ± 185                                                                           --                                    21435  50     0.2 ± 0.1                                                                              <.001  395 ± 116                                                                            <.05                                        150     2 ± 1   NS     429 ± 132                                                                            <.05                                  21436  50     116 ± 20                                                                               <.001  3471 ± 229                                                                           <.001                                       150     144 ± 37                                                                               <.01   1458 ± 424                                                                           NS                                    21437  50     47 ± 8  <.001  1707 ± 518                                                                           NS                                          150     111 ± 26                                                                               <.01   2799 ± 783                                                                           NS                                    20723  50     120 ± 16                                                                               <.001  3099 ±  361                                                                          <.001                                       150     122 ± 19                                                                               <.001  3064 ± 677                                                                           <.05                                         50     71 ± 8  <.001  1273 ± 279                                                                           NS                                          150     151 ± 17                                                                               <.001  3472 ± 538                                                                           <.01                                  21435 D-3-Pal.sup.6 --LHRH--C.sub.3 H.sub.7                                    21436 D-3-Pal.sup.6 --LHRH--C.sub.2 H.sub.5                                    21437 D-3-Pal.sup.6 --LHRH--CH.sub.3                                           21423 D-3-Pal.sup.6 --LHRH                                                     20700 D-3-Qal.sup.6 --LHRH                                                     ______________________________________                                          Mean of 6 ± SEM P values compared to respective dose of LHRH. Blood         sample at ±60 minutes after injection of saline or peptide sc.        

                                      TABLE X                                      __________________________________________________________________________     IN VIVO Assay in Rats                                                          for Release of LH and FSH:                                                     21 Day-Old Females                                                                            LH ng/ml     FSH ng/ml                                                    Dose Serum ± SEM at                                                                           Serum ± SEM at                                  Peptide   ng/rat sc                                                                           +120 min p value                                                                            +120 min p value                                   __________________________________________________________________________               --    0.2 ± 0.1                                                                               332 ± 50                                                                             --                                        D-Pal.sup.6 --NH--C.sub.2 H.sub.5                                                         50  291 ± 11                                                                             --  4692 ± 393                                                                           --                                        D-Pal.sup.6 --NH--C.sub.2 H.sub.5                                                        150  278 ± 14                                                                             --  4811 ± 782                                                                           --                                        D-Pal.sup.6 --LHRH                                                                        50  111 ± 26                                                                             <.001                                                                              3251 ± 485                                                                           NS                                        D-Pal.sup.6 --LHRH                                                                       150  216 ± 46                                                                             NS  5293 ± 686                                                                           NS                                        Mean of 6 ± SEM                                                             __________________________________________________________________________

                                      TABLE XI                                     __________________________________________________________________________     IN VIVO Assay in Rats for                                                      Release of LH and FSH                                                          21-Day Old Females                                                             __________________________________________________________________________                   +2 hrs        +3 hrs                                                           LH ± SEM   LH ± SEM                                        Peptide Dose-sc                                                                              ng/ml serum                                                                            p value                                                                              ng/ml serum                                                                            p value                                    __________________________________________________________________________     0.15    --    <0.1           0.24 ± 0.14                                    LHRH    150 ng                                                                                .18 ± 0.07                                                                         <.001  0.66 ± 0.46                                                                        <.001                                      20723    50 ng                                                                               108 ± 17                                                                            NS      20 ± 2.3                                                                          NS                                         20723   150 ng                                                                               144 ± 27                                                                            --      38 ± 6.3                                                                          --                                         21436   150 ng                                                                               237 ± 52                                                                            NS    106 ± 13                                                                            <.01                                       27000   150 ng                                                                               156 ± 7                                                                             NS    104 ± 23                                                                            <.05                                       CDB 8600                                                                               150 ng                                                                               230 ± 41                                                                            NS    117 ± 9                                                                             <.001                                      83-256-50                                                                              150 ng                                                                               184 ± 29                                                                            NS    103 ± 9                                                                             <.001                                      __________________________________________________________________________                   FSH ± SEM  FSH ± SEM                                       Peptide Dose-sc                                                                              ng/ml serum                                                                            p value                                                                              ng/ml serum                                                                            p value                                    __________________________________________________________________________     0.1% gel                                                                               --    147 ± 19                                                                            <.001 361 ± 38                                                                            <.001                                      LHRH    150 ng                                                                               337 ± 20                                                                            <.001 487 ± 72                                                                            <.001                                      20723    50 ng                                                                               1727 ± 222                                                                          NS    1312 ± 163                                                                          NS                                         20723   150 ng                                                                               2362 ± 293                                                                          --    1617 ± 143                                                                          --                                         21436   150 ng                                                                               2415 ± 361                                                                          NS    2205 ± 298                                                                          NS                                         27000   150 ng                                                                               2211 ± 160                                                                          NS    2376 ± 529                                                                          NS                                         CDB 8600                                                                               150 ng                                                                               2332 ± 388                                                                          NS    2065 ± 151                                                                          NS                                         83-256-50                                                                              150 ng                                                                               2260 ± 294                                                                          NS    1763 148                                                                               NS                                         Mean 5-6 ± SEM                                                              20723 pyroGlu--His--Trp--Ser--Tyr--D-Pal*--Leu--Arg--Pro--Gly--NH.sub.2        21436 pyroGlu--His--Trp--Ser--Tyr--D-Pal*--Leu--Arg--Pro--EA**                 27000 pyroGlu--His--Trp--Ser--Tyr--D-Qal***--Leu--Arg--Pro--Gly--NH.sub.2            3                                                                        CDB 8600                                                                             pyroGlu--His--Trp--Ser--Tyr--D-Trp--Leu--Arg--Pro--Gly--NH.sub.2         83-256-50                                                                            pyroGlu--His--Trp--Ser--Tyr-- D-Trp--Leu--Arg--Pro--EA**                 __________________________________________________________________________      *D-3-Pal = 3(3-Pyridyl)-D-Ala                                                  **EA = ethylamide                                                              ***D3-Qal = 3(3-Quinolyl)-D-Ala                                           

What is claimed:
 1. pyroGlu-His-Trp-Ser-Tyr-D- 3-Pal-Leu-Arg-Pro-Gly-NH₂.
 2. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHCH₃.
 3. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHC₂ H₅.
 4. pyroGlu-His-Trp-Ser-Tyr-D-3-Pal-Leu-Arg-Pro-NHC₃ H₇. 